The three dimensional epoxy-amine network produced by the curing of amine/epoxy resin formulations is well known to exhibit desirable mechanical, chemical, thermal and other properties. As a result, amine curable epoxy resins systems have been widely used as coatings, adhesives, sealants and matrices for fiber-reinforced composites. Epoxy resin systems are also particularly useful in the preparation of composite articles by wet filament winding techniques. In many instances, however, it is not always possible to prepare articles by wet filament winding wherein the starting liquid in which the filaments are coated is of sufficiently low viscosity for use in presently available coating equipment, and yet which results in a finished, cured product having the optimum desired properties. In many instances, the viscosity of the resin solution must be adjusted by the addition of diluents which adversely effect the thermal and mechanical properties of the resulting product.
For example, in U.S. Pat. No. 4,517,321 which issued May 14, 1985 high strength, high modulus materials are disclosed which have low water uptake properties but are not suitable for wet filament winding techniques due to their high viscosities. In this patent the compositions disclosed are comprised of an epoxy resin containing two or more 1,2-epoxide groups per molecule, a structural fiber and a diamine hardener. The diamine hardeners which are disclosed as being useful in preparing the compositions of the invention are characterized by the presence of four aromatic rings in the diamine molecule and which are separated from each other by divalent groups such as oxygen, sulfur, sulfur dioxide, carbonyl, ester and like groups. However, as indicated, the resin systems disclosed are not adequate for use in preparing composite articles by wet filament winding techniques due to their high viscosities at ambient temperature. Accordingly, there is a need for a resin system which has the desired viscosity for wet winding procedures without the need for diluents and which also results in cured products having the desired characteristics for a particular application.
It has now been found that by using a resin system as hereinafter described, articles can be prepared by the wet winding process and which also result in cured systems having optimum physical and other properties.